Chapter 1 introduction

Software Engineering (3rd ed.), By K.K Aggarwal & Yogesh Singh, Copyright © New Age International Publishers, 2007
1

2
Why Software Engineering ?Why Software Engineering ?Why Software Engineering ?Why Software Engineering ?
Change in nature & complexity of software
Ready for change
Concept of one “guru” is over
We all want improvement

3
Software industry is in Crisis!
Source: The Standish Group International, Inc. (CHAOS research)
over budget
53%
success
16%failure
31%
The Evolving Role of SoftwareThe Evolving Role of SoftwareThe Evolving Role of SoftwareThe Evolving Role of Software

4
• Data on 28,000 projects
completed in 2000
This is the
SORRY state
of Software
Engineering
Today!
Completed
Late, over
budget, and/or
with features
missing – 49%
Cancelled –
23%
Successful –
28%

5
As per the IBM report, “31%of the project get
cancelled before they are completed, 53% over-
run their cost estimates by an average of 189%
and for every 100 projects, there are 94 restarts”.

6
Year
Hw cost
Sw cost
Relative Cost of Hardware and Software
1960 1999

7
• Unlike Hardware
– Moore’s law: processor speed/memory capacity doubles
every two years

8
Managers and Technical Persons are asked:
Why does it take so long to get the program finished?
Why are costs so high?
Why can not we find all errors before release?
Why do we have difficulty in measuring progress of software
development?

9
Factors Contributing to the Software CrisisFactors Contributing to the Software CrisisFactors Contributing to the Software CrisisFactors Contributing to the Software Crisis
• Larger problems,
• Lack of adequate training in software engineering,
• Increasing skill shortage,
• Low productivity improvements.

10
Some Software failuresSome Software failuresSome Software failuresSome Software failures
It took the European Space Agency 10
years and $7 billion to produce Ariane 5,
a giant rocket capable of hurling a pair of
three-ton satellites into orbit with each
launch and intended to give Europe
overwhelming supremacy in the
commercial space business.
Ariane 5
The rocket was destroyed after 39 seconds
of its launch, at an altitude of two and a
half miles along with its payload of four
expensive and uninsured scientific
satellites.

11
When the guidance system’s own
computer tried to convert one
piece of data the sideways velocity
of the rocket from a 64 bit format
to a 16 bit format; the number was
too big, and an overflow error
resulted after 36.7 seconds. When
the guidance system shutdown, it
passed control to an identical,
redundant unit, which was there to
provide backup in case of just such
a failure. Unfortunately, the second
unit, which had failed in the
identical manner a few
milliseconds before.

12
Y2K problem:
It was simply the ignorance about the
adequacy or otherwise of using only
last two digits of the year.
The 4-digit date format, like 1964,
was shortened to 2-digit format, like
64.

13
The Patriot MissileThe Patriot MissileThe Patriot MissileThe Patriot Missile
o First time used in Gulf war
Reasons:
A small timing error in the system’s clock
accumulated to the point that after 14
hours, the tracking system was no longer
accurate. In the Dhahran attack, the
system had been operating for more than
100 hours.
o Used as a defense from Iraqi Scud
missiles
o Failed several times including one that
killed 28 US soldiers in Dhahran,
Saudi Arabia

14
Part of an abort scenario for the
Shuttle requires fuel dumps to
lighten the spacecraft. It was
during the second of these
dumps that a (software) crash
occurred.
...the fuel management module,
which had performed one
dump and successfully exited,
restarted when recalled for the
second fuel dump...
The Space Shuttle

15
A simple fix took care of the problem…but the
programmers decided to see if they could come up with a
systematic way to eliminate these generic sorts of bugs in
the future. A random group of programmers applied this
system to the fuel dump module and other modules.
Seventeen additional, previously unknown problems
surfaced!

16
Many companies have experienced failures in their
accounting system due to faults in the software itself. The
failures range from producing the wrong information to
the whole system crashing.
Financial Software

17
Windows XP
o Microsoft released Windows XP on October 25, 2001.
o On the same day company posted 18 MB of
compatibility patches on the website for bug fixes,
compatibility updates, and enhancements.
o Two patches fixed important security holes.
This is Software Engineering.

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The hardware cost continues to decline
drastically.
““““No Silver BulletNo Silver BulletNo Silver BulletNo Silver Bullet””””
However, there are desperate cries for a
silver bullet something to make software
costs drop as rapidly as computer hardware
costs do.
But as we look to the horizon of a decade,
we see no silver bullet. There is no single
development, either in technology or in
management technique, that by itself
promises even one order of magnitude
improvement in productivity, in reliability
and in simplicity.

19
The hard part of building software is the specification, design and
testing of this conceptual construct, not the labour of representing it
and testing the correctness of representation.
While there is no royal road, there is a path forward.
Is reusability (and open source) the new silver bullet?
We still make syntax errors, to be sure, but they are trivial as
compared to the conceptual errors (logic errors) in most systems.
That is why, building software is always hard and there is inherently
no silver bullet.

20
The blame for software bugs belongs to:
• Software companies
• Software developers
• Legal system
• Universities

21
What is software?What is software?What is software?What is software?
• Computer programs and associated
documentation

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Programs
Operating
Procedures
Documentation
Software=Program+Documentation+Operating Procedures
Components of software
What is software?What is software?What is software?What is software?

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Documentation
Manuals
Analysis
/Specification
Design
Implementation
Testing
Formal Specification
Context-
Diagram
Data Flow
Diagrams
Flow Charts
Entity-Relationship
Diagram
Source Code Listings
Cross-Reference
Listing
Test Data
Test Results
Documentation consists of different types of manuals areDocumentation consists of different types of manuals areDocumentation consists of different types of manuals areDocumentation consists of different types of manuals are
List of documentation manuals

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Operating
Procedures
User
Manuals
Operational
Manuals
System Overview
Beginner’s Guide
Tutorial
Reference Guide
Installation Guide
System
Administration Guide
List of operating procedure manuals.
Documentation consists of different types of manuals areDocumentation consists of different types of manuals areDocumentation consists of different types of manuals areDocumentation consists of different types of manuals are

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• Software products may be developed for a particular
customer or may be developed for a general market
Software ProductSoftware ProductSoftware ProductSoftware Product
• Software products may be
–Generic - developed to be sold to a range of different
customers
–Bespoke (custom) - developed for a single customer according
to their specification

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Software product is a product designated for
delivery to the user
source
codes
source
codes
object
codes
object
codes
plansplans
reportsreports
manualsmanuals
documentsdocuments
test suitestest suites
prototypesprototypes
datadata
test resultstest results
Software ProductSoftware ProductSoftware ProductSoftware Product

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What is software engineering?What is software engineering?What is software engineering?What is software engineering?
Software engineering is an engineering discipline which
is concerned with all aspects of software production
Software engineers should
– adopt a systematic and organised approach to their
work
– use appropriate tools and techniques depending on
• the problem to be solved,
• the development constraints and
– use the resources available

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At the first conference on software engineering in 1968, Fritz Bauer
defined software engineering as “The establishment and use of
sound engineering principles in order to obtain economically
developed software that is reliable and works efficiently on real
machines”.
Stephen Schach defined the same as “A discipline whose aim is the
production of quality software, software that is delivered on time,
within budget, and that satisfies its requirements”.
Both the definitions are popular and acceptable to majority.
However, due to increase in cost of maintaining software, objective
is now shifting to produce quality software that is maintainable,
delivered on time, within budget, and also satisfies its requirements.
What is software engineering?What is software engineering?What is software engineering?What is software engineering?

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Software ProcessSoftware ProcessSoftware ProcessSoftware Process
The software process is the way in which we produce
software.
Why is it difficult to improve software process ?
• Not enough time
• Lack of knowledge

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Learning curve
Do not quit here!
Improved future state
Process improvement
begins
Initial state
state
Productivity
Time
• Wrong motivations
Software ProcessSoftware ProcessSoftware ProcessSoftware Process
• Insufficient commitment

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Software Characteristics:Software Characteristics:Software Characteristics:Software Characteristics:
Software does not wear out.
Useful life
phase
Wear out
phase
Burn-in
phase
FailureIntensity
Time

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Software is not manufactured
Reusability of components
Software is flexible

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Comparison of constructing a bridge vis-à-vis writing a program.
7.
6.
5.
4.
3.
2.
1.
Writing a programConstructing a bridgeSr.
No
The problem is well understood
Only some parts of the problem are
understood, others are not
There are many existing bridges
The requirement for a bridge typically do
not change much during construction
The strength and stability of a bridge can be
calculated with reasonable precision
When a bridge collapses, there is a
detailed investigation and report
Engineers have been constructing bridges
for thousands of years
Materials (wood, stone,iron, steel) and
techniques (making joints in wood, carving
stone, casting iron) change slowly.
Every program is different and designed for
special applications.
Requirements typically change during all
phases of development.
Not possible to calculate correctness of a
program with existing methods.
When a program fails, the reasons are often
unavailable or even deliberately concealed.
Developers have been writing programs
for 50 years or so.
Hardware and software changes rapidly.

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System
Software
Real
Time
Software
Embedded
Software
Engineering
and Scientific
Software
Web based
Software
Artificial
Intelligence
Software
Personal
Computer
Software
Business
Software
The Changing Nature of SoftwareThe Changing Nature of SoftwareThe Changing Nature of SoftwareThe Changing Nature of Software

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The Changing Nature of SoftwareThe Changing Nature of SoftwareThe Changing Nature of SoftwareThe Changing Nature of Software
Trend has emerged to provide source code to the
customer and organizations.
Software where source codes are available are known
as open source software.
Examples
Open source software: LINUX, MySQL, PHP, Open office,
Apache webserver etc.

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Management may be confident about good
standards and clear procedures of the company.
But the taste of any food item
is in the eating;
not in the Recipe !
Software Myths (Management PerspectivesSoftware Myths (Management PerspectivesSoftware Myths (Management PerspectivesSoftware Myths (Management Perspectives)

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Company has latest computers and state-of-
the-art software tools, so we shouldn’t worry
about the quality of the product.
The infrastructure is
only one of the several factors
that determine the quality
of the product!

38
Addition of more software specialists, those
with higher skills and longer experience may
bring the schedule back on the track!
Unfortunately,
that may further delay the schedule!

39
Software is easy to change
The reality is totally different.

40
Computers provide greater reliability than
the devices they replace
This is not always true.

41
A general statement of objectives is sufficient to get started with
the development of software. Missing/vague requirements can
easily be incorporated/detailed out as they get concretized.
If we do so, we are heading
towards a disaster.
Software Myths (Customer PerspectivesSoftware Myths (Customer PerspectivesSoftware Myths (Customer PerspectivesSoftware Myths (Customer Perspectives)

42
Software with more features is better
software
Software can work right the first time
Both are only myths!
Software Myths (Customer PerspectivesSoftware Myths (Customer PerspectivesSoftware Myths (Customer PerspectivesSoftware Myths (Customer Perspectives)

43
Once the software is demonstrated, the job is done.
Usually, the problems just begin!
Software Myths (Developer PerspectivesSoftware Myths (Developer PerspectivesSoftware Myths (Developer PerspectivesSoftware Myths (Developer Perspectives)

44
Software quality can not be assessed before
testing.
However, quality assessment techniques
should be used through out the
software development life cycle.

45
The only deliverable for a software
development project is the tested code.
Tested code is only one of the deliverable!

46
Aim is to develop working programs
Those days are over. Now objective is to
develop good quality maintainable
programs!

47
Some TerminologiesSome TerminologiesSome TerminologiesSome Terminologies
Deliverables and Milestones
Different deliverables are generated during software development.
The examples are source code, user manuals, operating procedure
manuals etc.
The milestones are the events that are used to ascertain the status of
the project. Finalization of specification is a milestone. Completion of
design documentation is another milestone. The milestones are
essential for project planning and management.

48
Product and Process
Product: What is delivered to the customer, is called a product. It
may include source code, specification document, manuals,
documentation etc. Basically, it is nothing but a set of deliverables
only.
Process: Process is the way in which we produce software. It is the
collection of activities that leads to (a part of) a product. An efficient
process is required to produce good quality products.
If the process is weak, the end product will undoubtedly suffer, but
an obsessive over reliance on process is also dangerous.

49
Measures, Metrics and Measurement
A measure provides a quantitative indication of the extent,
dimension, size, capacity, efficiency, productivity or reliability of
some attributes of a product or process.
Measurement is the act of evaluating a measure.
A metric is a quantitative measure of the degree to which a system,
component or process possesses a given attribute.

50
Software Process and Product Metrics
Process metrics quantify the attributes of software development
process and environment;
whereas product metrics are measures for the software product.
Examples
Process metrics: Productivity, Quality, Efficiency etc.
Product metrics: Size, Reliability, Complexity etc.

51
Productivity and Effort
Productivity is defined as the rate of output, or production per unit of
effort, i.e. the output achieved with regard to the time taken but
irrespective of the cost incurred.
Hence most appropriate unit of effort is Person Months (PMs),
meaning thereby number of persons involved for specified months.
So, productivity may be measured as LOC/PM (lines of code
produced/person month)

52
Module and Software Components
There are many definitions of the term module. They range from “a
module is a FORTRAN subroutine” to “a module is an Ada
Package”, to “Procedures and functions of PASCAL and C”, to
“C++ Java classes” to “Java packages” to “a module is a work
assignment for an individual developer”. All these definition are
correct. The term subprogram is also used sometimes in place of
module.

53
“An independently deliverable piece of functionality providing
access to its services through interfaces”.
“A component represents a modular, deployable, and replaceable
part of a system that encapsulates implementation and exposes a set
of interfaces”.

54
Generic and Customized Software Products
Generic products are developed for anonymous customers. The target
is generally the entire world and many copies are expected to be sold.
Infrastructure software like operating system, compilers, analyzers,
word processors, CASE tools etc. are covered in this category.
The customized products are developed for particular customers.
The specific product is designed and developed as per customer
requirements. Most of the development projects (say about
80%)come under this category.

55
Role of Management in Software Development
Factors
People
Product Process
Project

56
Dependency
Order
Project Product
Process
People
1
2
3
4
Role of Management in Software Development

57
1.1 Software is
(a) Superset of programs (b) subset of programs
(c) Set of programs (d) none of the above
1.2 Which is NOT the part of operating procedure manuals?
(a) User manuals (b) Operational manuals
(c) Documentation manuals (d) Installation manuals
1.3 Which is NOT a software characteristic?
(a) Software does not wear out (b) Software is flexible
(c) Software is not manufactured (d) Software is always correct
1.4 Product is
(a) Deliverables (b) User expectations
(c) Organization's effort in development (d) none of the above
Multiple Choice Questions
Note: Select most appropriate answer of the following questions:
1.5 To produce a good quality product, process should be
(a) Complex (b) Efficient
(c) Rigorous (d) none of the above

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1.6 Which is not a product metric?
(a) Size (b) Reliability
(c) Productivity (d) Functionality
1.7 Which is NOT a process metric?
(a) Productivity (b) Functionality
(c) Quality (d) Efficiency
1.8 Effort is measured in terms of:
(a) Person-months (b) Rupees
(c) Persons (d) Months
1.9 UML stands for
(a) Uniform modeling language (b) Unified modeling language
(c) Unit modeling language (d) Universal modeling language
1.1 An independently deliverable piece of functionality providing access to
its services through interface is called
(a) Software measurement (b) Software composition
(c) Software measure (d) Software component

59
1.11 Infrastructure software are covered under
(a) Generic products (b) Customized products
(c) Generic and Customized products (d) none of the above
1.12 Management of software development is dependent on
(a) people (b) product
(c) process (d) all of the above
1.13 During software development, which factor is most crucial?
(a) People (b) Product
(c) Process (d) Project
1.14 Program is
(a) subset of software (b) super set of software
(c) software (d) none of the above
1.15 Milestones are used to
(a) know the cost of the project (b) know the status of the project
(c) know user expectations (d) none of the above

60
1.16 The term module used during design phase refers to
(a) Function (b) Procedure
(c) Sub program (d) All of the above
1.17 Software consists of
(a) Set of instructions + operating system
(b) Programs + documentation + operating procedures
(c) Programs + hardware manuals (d) Set of programs
1.18 Software engineering approach is used to achieve:
(a) Better performance of hardware (b) Error free software
(c) Reusable software (d) Quality software product
1.19 Concept of software engineering are applicable to
(a) Fortran language only (b) Pascal language only
(c) ‘C’ language only (d) All of the above
1.20 CASE Tool is
(a) Computer Aided Software Engineering (b) Component Aided Software Engineering
(c) Constructive Aided Software Engineering (d)Computer Analysis Software Engineering

61
Exercises
1.1 Why is primary goal of software development now shifting from
producing good quality software to good quality maintainable software?
1.2 List the reasons for the “software crisis”?Why are CASE tools not
normally able to control it?
1.3 “The software crisis is aggravated by the progress in hardware
technology?” Explain with examples.
1.4 What is software crisis? Was Y2K a software crisis?
1.5 What is the significance of software crisis in reference to software
engineering discipline.
1.6 How are software myths affecting software process? Explain with the
help of examples.
1.7 State the difference between program and software. Why have documents
and documentation become very important.
1.8 What is software engineering? Is it an art, craft or a science? Discuss.

62
Exercises
1.9 What is aim of software engineering? What does the discipline of
software engineering discuss?
1.10 Define the term “Software engineering”. Explain the major differences
between software engineering and other traditional engineering disciplines.
1.11 What is software process? Why is it difficult to improve it?
1.12 Describe the characteristics of software contrasting it with the
characteristics of hardware.
1.13 Write down the major characteristics of a software. Illustrate with a
diagram that the software does not wear out.
1.14 What are the components of a software? Discuss how a software differs
from a program.
1.15 Discuss major areas of the applications of the software.
1.16 Is software a product or process? Justify your answer with example

63
Exercises
1.17 Differentiate between the following
(i) Deliverables and milestones (ii) Product and process
(iii) Measures, metrics and measurement
1.18 What is software metric? How is it different from software
measurement
1.19 Discuss software process and product metrics with the help of examples.
1.20 What is productivity? How is it related to effort. What is the unit of
effort.
1.21 Differentiate between module and software component.
1.22 Distinguish between generic and customized software products. Which
one has larger share of market and why?
1.23 Is software a product or process? Justify your answer with example

64
1.23 Describe the role of management in software development with the help
of examples.
1.24 What are various factors of management dependency in software
development. Discuss each factor in detail.
1.25 What is more important: Product or process? Justify your answer.
Exercises

Chapter 1 introduction

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